The invention relates to a loudspeaker with a cone and with a beading attached to the cone as well as to a process for manufacturing a loudspeaker.
Loudspeakers of the previously documented state of the art are dynamic loudspeakers in which a moving coil moves within the magnetic field of a permanent magnet in response to electrical signals. In this way, a cone attached to the coil is set into motion and generates soundwaves. The cone sets the surrounding air into a motion which most closely corresponds to the electrical signal and in which no audible vibrations due to the cone itself should be generated. The cone itself must exhibit a high degree of inner dampening. It is for this reason that the state of the art uses a fibrous paper mixture, polymer, metal foam or metal, preferably in a honeycomb structure, for the material of the cone.
In order that the cone can carry out its movement in as unimpeded a manner as possible, it is neccessary to attach the outer edge of the cone with a loudspeaker frame by means of a beading which holds the cone with the highest possible constant resilience in the predetermined direction of movement. Here, it is generally known that the beading is composed of rubber, foam or greased weaving.
EP 0 552 040 B1, upon which the present invention is based, discloses a loudspeaker with a cone composed of rigid polypropylene. The beading attached to the cone is on the other hand made of a soft polymer material, so that the different requirements of the rigidity of the cone material on the one hand and of the beading on the other are met. In the first step of the manufacture of this loudspeaker, the cone is placed or solidly clamped into the mold, followed by injection of elastomeric material into the mold. It is also disclosed that the cone is first manufactured by injection of a material made of polypropylene, followed by the manufacture of the beading by injection of elastomeric material.
A loundspeaker is also known from EP 0 632 674 A1, the cone of which is composed of polypropylene, and the beading and associated contact portion of which is composed of a thermoplastic synthetic resin. Dichromatic molding is employed in the manufacture, in the first step of which the polypropylene cone is manufactured in the mold. In the second process step, the beading and the contact portion with a seal are manufactured by injection of thermoplastic resin into the mold. During the curing of the materials, these parts join with one another at the attachment point provided so that a permanent attachment is formed.
Finally, a loudspeaker is known from EP 0 632 675 A1 in which both the cone as well as the beading are composed of woven materials, which however are treated by different amounts of a thermoplastic resin. This results in differing rigidities for the cone and the bead.
The loudspeakers described above in the state of the art have the disadvantage that the elastic properties of the materials used are only adjustable to a limited extent. For this reason, it is necessary that different materials be used for the cone and the bead. Furthermore, in the event that loudspeakers of varying specification are manufactured, it is not possible to use the same materials in the manufacture of the different loudspeakers. It is also disadvantageous in the manufacturing processes known from the state of the art that closed molds in which the material is injected have to be used for each process. These manufacturing processes have the further disadvantage that considerable waste is generated as a result of the excess material.
A process is known from EP 0 379 246 B1 for the manufacture and use of a sprayable polyurethane material. In this process, a polyurethane reaction mixture composed of two components is made which is sprayed onto the surface of a negative mold in order to make a film of uniform thickness. To this end, the spray gun comprises a nozzle for each component, out of which the respective components exit. The characteristics of the sprayed polyurethane layer can be variably tuned by setting the flowthrough amount of each of the components through its respective nozzle. In particular, the rigidity of the polyurethane film is amenable to adjustment within a wide range. The process described in EP 0 379 246 B1 facilitates in particular the manufacture of instrument panel components in auto manufacturing.
The underlying technical problem addressed by the present invention is to provide a loudspeaker and a process for the production of a loudspeaker, which avoid the disadvantages of the state of the art described above.
The technical problem described above is solved according to the invention by a cone with a beading attached to the cone, in which the beading is composed of a sprayable plastic layer which is soft in its solidified state. This offers the advantage that the elasticity of the beading can be very precisely adjusted to meet particular requirements. This is important because the elasticity requirement for the beading for a loudspeaker depends not only on the size of the loudspeaker but also on the amplitude at which the cone is to be able to move. In a first preferred embodiment, the plastic layer is composed of a thermoplastic material. However, if the layer is composed of a two-component reaction mixture as in a second preferred embodiment, the elasticity of the beading according to the invention can be very precisely tuned to the specific application by adjusting the amounts of the components in the polyurethane layer.
The beading preferably contains one or more of the materials polyurethane, polypropylene, polyvinylchloride or polyethylene.
Due to the purity of the types, the beading is preferably made of a polyurethane layer.
A further advantage of using the materials named above, especially polyurethane, is the fact that the beading made therefrom is watertight, allowing values of 50 mm WS and higher to be achieved. The loudspeaker can therefore be reliably used in locations where the danger of contact with moisture exists. As an example of such locations, car doors are hereby cited.
In a further preferred embodiment, the cone is composed of the same material as the beadingxe2x80x94in the especially preferred embodiment a polyurethane layerxe2x80x94which, in contrast to the bead, is rigid, and which exhibits such sufficient stiffness as is needed to fulfill the requirements for sound generation by the loudspeaker. When both the cone as well as the beading are composed of a polyurethane layer, a further advantageous purity of type can therefore be achieved in the components of the loudspeaker, thereby simplifying any later disposal or recycling.
Furthermore, the manufacturing process described below ensures the formation of an integral attachment between the cone and the bead, thereby advantageously avoiding the need for glues.
A further advantage results from the provision of a seal attached to the bead, whereby an integral attachment between the beading and the seal is also preferentially provided.
The above mentioned underlying technical problem addressed by the invention is further solved by a process for the manufacture of a loudspeaker using an open negative mold which predetermines the shape of a loudspeaker composed of cone and bead. The cone, which can be made in advance and can be composed of known materials, is situated in the mold and is immobilized in its correct position. This is followed by the process according to the invention, in which a sprayable plastic is sprayed into the open negative mold, thereby forming a beading as a soft plastic layer which adheres to the cone. A thermoplastic plastic can be used. However, when a plastic composed of a two-component reaction mixture is used, the elasticity of the beading can be very precisely tuned to correspond to the shape, size and performance requirements of the loudspeaker by suitable choice of the mixture ratio of the two components. It is especially preferable that the plastic be composed of a two-component polyurethane reaction mixture.
In a preferred embodiment of the process according to the invention, the cone is similarly made of a polyurethane layer which is however of a higher rigidity than the beading described earlier. In the manufacture of the cone, a polyurethane reaction mixture consisting of two components is similarly sprayed into the open negative mold and is trimmed after curing. Preferably, the cone and the beading are made in this way in two subsequent process steps by spraying a polyurethane reaction mixture composed of two components in the same negative mold. Since the cone and the beading are accordingly made of essentially the same materials of only varying rigidity, a solid integral attachment is formed between the cone and the beading at the corresponding attachment point.
If the cone is made separately prior to the making of the bead, the cone can be situated and positioned in the negative mold both before as well as after the spraying of the polyurethane layer for the manufacture of the bead. In either case, a solid attachment between the cone and the beading is made during curing, eliminating the need to make a separate glue attachment.
A further improvement of the process according to the invention is achieved by the setting of a sealing ring into a recess provided in the negative mold prior to spraying the polyurethane layer for the manufacture of the bead. If the polyurethane layer is sprayed onto the negative mold as well as onto the side of the sealing ring facing the open side of the negative mold, then a solid attachment is formed between the beading and the sealing ring during curing of the polyurethane layer. The use of a glue can be avoided here as well.
Preferably, the process according to the invention is further simplified by the use of rotationally symmetric negative molds, in that the negative mold is rotated during the spraying of the polyurethane layer and that the spray head carries out an essentially linear movement. Uniformity of application of the polyurethane layer can be ensured by means of a suitable synchronization between the rotational movement and the linear movement, so that the most uniform polyurethane layer possible results.
The maintenance of a predetermined layer thickness is further achieved by the use of a countermold matched to the negative mold which is applied to the polyurethane layer following spraying in order to yield a precisely defined thickness in the polyurethane layer. In this way, the polyurethane layer, which is still fluid following spraying, is trapped between the negative mold and the countermold, which exhibit a predetermined separation from one another. Following curing, a polyurethane layer with a precisely defined thickness is formed.
So that the countermold and the negative mold can each be removed from the manufactured polyurethane layer, it is advantageous to coat those sides of the countermold and the negative mold which face towards the polyurethane layer with a non-stick agent.
The amount of non-stick agent can be reduced or, in the case of the negative mold, the use of a non-stick agent can be avoided altogether, if apertures are provided in the negative mold, through which pressurized air can be fed to simplify the freeing from the mold. In this way, one can particularly guarantee that there is no non-stick agent present in the regions where the formation of an attachment of the polyurethane layer with a seal positioned in a recess of the negative mold is intended, which could otherwise impede such an attachment.